docs: def run_cmd_unit(self, sentry_unit, cmd):
          """Run a command on a unit, return the output and exit code."""
          output, code = sentry_unit.run(cmd)
          if code == 0:
              self.log.debug('{} `{}` command returned {} '
                             '(OK)'.format(sentry_unit.info['unit_name'],
                                           cmd, code))
          else:
              msg = ('{} `{}` command returned {} '
                     '{}'.format(sentry_unit.info['unit_name'],
                                 cmd, code, output))
              amulet.raise_status(amulet.FAIL, msg=msg)
          return str(output), code